Cartridge breakin ......how long?

120 - 150 hours with Koetsu. The suspension also needs break in, so you can put the tonearm on the LP, when the turntable is not in use.

I have a Soundsmith Aida and it took between 50 to 100
hours of playing time be patience you will be rewarded with great sound.

i like it when it's out of box just like new strings on guitar tho

IMO, it depends on the cartridge. My experience with various cartridges is between 20 and 200 hours to reach best performance.

ALSO, at least in the case of an AT OC9/(all of them), if they sit idle for a while (week or more), it may take them a few record sides to get back to optimum. Regular play keeps them loose.

Thanks for the input. Cartridge was mounted by experienced dealer. I will wait 50 hours and then make adjustments. I'm excited about this cartridge's potential. Tracks very quietly and retrieves more info out-of-the-box than my Glider. Can't wait to hear it after breakin.